1. Field of the Invention
The present invention relates to an input device and a method of manufacturing the input device, and more particularly, to an input device that can improve environmental resistance and a method of manufacturing the input device.
2. Description of the Related Art
Currently, a translucent input device is used as a display portion of an electronic device such as a mobile phone. An input device is disposed so as to overlap a display device such as liquid crystal, and a user can be in visual contact with an image, which is displayed on the display device, through the input device. Further, a user can input position information by touching an input region with a finger or an input tool.
There are several types as the operation type of the input device. However, a capacitive input device is disclosed in, for example, Japanese Patent Application No. 2010-159334. FIG. 13 is an exploded perspective view of an input device 101 in the related art. In the capacitive input device 101, first and second transparent bases 130 and 140 are disposed so as to face each other and are bonded to each other with an optical adhesive layer (not shown) interposed therebetween. Further, a surface member 110, which protects the surface of the input device, is laminated on the surface of the first transparent base 130 close to an input surface, and is bonded to the first transparent base 130 with an optical adhesive layer (not shown) interposed therebetween.
First and second transparent electrode layers 131 and 141 are laminated on input regions 121 of the first and second transparent bases 130 and 140, respectively. Accordingly, when an operator makes a finger or the like be close to an arbitrary position on the input region 121, a value of capacitance between the transparent electrode layers is changed. The capacitive input device 101 can detect input position information on the basis of the change of the value of capacitance thereof.
As shown in FIG. 13, first and second connection electrodes 133 and 143 are provided in Y2-side portions of non-input regions 122 of the respective transparent bases, respectively. The first connection electrodes 133 are electrically connected to the first transparent electrode layer 131 through first lead electrodes 132 wired in the non-input region 122, and the second connection electrodes 143 are electrically connected to the second transparent electrode layer 141 through second lead electrodes 142. Further, the first and second connection electrodes 133 and 143 are connected to a flexible printed circuit board 163 (hereinafter, referred to as a FPC 163), so that input position information is output to the outside.
In Japanese Patent Application No. 2010-159334, the detailed structures of the FPC 163 and the respective connection electrodes were not disclosed and problems in the vicinity of a connecting portion were not considered. FIG. 14 is a schematic cross-sectional view of the vicinity of the FPC 163 and the respective connection electrodes of the input device 101 in the related art. The FPC 163 is disposed so that a predetermined gap is formed between the FPC 163 and the first optical adhesive layer 151 in plan view. The FPC 163 is bonded to the connection electrodes in a space between the first transparent base 130 and the surface member 110 facing each other. Accordingly, exposed portions 132a of the lead electrodes are exposed to a space between the first optical adhesive layer 151 and the FPC 163 facing each other. The lead electrodes 132 are made of a conductive material, such as silver or copper. For this reason, since the exposed portions 132a of the lead electrodes are affected by humidity, temperature, and the like of external air, there is a concern that disconnection caused by corrosion, a short circuit caused by the attachment of foreign materials, and the like may occur. Further, when the input device 101 is used for an in-vehicle electronic device, stricter environmental resistance is required.
A method of applying a sealing resin so as to cover the exposed portions of the electrodes is known as a method of preventing the defects of the exposed portions of the electrodes. For example, Japanese Unexamined Patent Application Publication No. 2002-250930 discloses an invention, which protects the surface of a wiring pattern exposed to a space between a liquid crystal panel and a FPC by overcoating the surface of the wiring pattern with a sealing resin, as for a liquid crystal display device.
The inventor examined a method of improving the environmental resistance of the input device 101 in the related art by sealing the exposed portions 132a of the lead electrodes with a resin so that the exposed portions 132a of the lead electrodes are covered. FIG. 15 is a schematic cross-sectional view of the input device 101 in the related art where a sealing resin 161 is applied on the exposed portions 132a of the lead electrodes and the surface member 110 is bonded.
The input device 101 shown in FIG. 15 is made by bonding the first optical adhesive layer 151 and the FPC 163 to the first transparent base 130, applying the sealing resin 161 to the exposed portions 132a of the lead electrodes by a dispenser, and bonding the surface member 110 thereto. However, since it is difficult to apply the sealing resin 161 while accurately controlling the thickness of the sealing resin 161, the sealing resin 161 is applied with a large thickness. For this reason, there may be a case where a protrusive step is formed on the first optical adhesive layer 151. There is a problem that a blister 164 is generated between the first optical adhesive layer 151 and the surface member 110 as shown in FIG. 15 when the flat surface member 110 is bonded to the first optical adhesive layer 151 and the sealing resin 161 having the protrusive step. If the blister 164 is generated, not only appearance quality deteriorates but also a change in a distance between the input surface and the transparent electrode layer and a change in permittivity occur. For this reason, there is a possibility that the sensitivity of a sensor of the input device 101 may deteriorate.